DelegateResult, an IActionResult useful for Azure Functions

DelegateResult.fs

open Microsoft.AspNetCore.Mvc

type DelegateResult(write : Stream -> System.Threading.Tasks.Task, encoding : System.Net.Http.Headers.MediaTypeHeaderValue, status : int) =
  interface IActionResult with
    member this.ExecuteResultAsync(ctx) =
      ctx.HttpContext.Response.StatusCode  <- status
      ctx.HttpContext.Response.ContentType <- encoding.ToString ()
      write ctx.HttpContext.Response.Body

open System.Text.Json

let private options  = JsonSerializerOptions()
let private encoding = System.Net.Http.Headers.MediaTypeHeaderValue "application/json"
encoding.CharSet <- System.Text.Encoding.UTF8.WebName

let serialize value = (fun stream -> JsonSerializer.SerializeAsync(stream, value, options)), encoding


let write, encoding = serialize {| thing = 42 |}
DelegateResult  (write, encoding, 200) :> IActionResult